The present invention relates to a method of increasing the efficiency of a system providing useful work, such as the generation of electrical power, using elevation and temperature differences on the surface of the earth.
In U.S. Pat. Nos. 3,945,218 and 3,953,971 to Parker, systems for performing useful work are disclosed which utilize the differences in elevation that are naturally provided by mountainous regions and nearby valleys or desert floors and the naturally available temperature differences that occur between them. The disclosed systems include condenser means located at the higher and cooler elevation of the mountain, and means (an evaporator or boiler) located at the lower and warmer elevation, in a valley or desert below the mountain, for supplying heat to the system. A working fluid capable of vaporizing at a relatively low temperature is employed as the mechanism for converting temperature and pressure differences into useful work. The fluid absorbs heat from the heat supply means, at the warmer elevation, vaporizes, and rises in a pipe or conduit connecting the heat supply means to the condenser. When the fluid (vapor) reaches the condenser, which is relatively cold, the vapor condenses and the resulting liquid returns under the force of gravity through another pipe to the turbine of a power generation means, for example, located at the lower elevation. After passing through the turbine, the condensate (liquid) is directed to the heat supply means for a repeat of the cycle.
A process related to the above process, which is a land-base method using temperature differences in the atmosphere, is a process that utilizes the difference in temperature and pressure occurring between the ocean surface, which is relatively warm, particularly in the tropics, and the ocean depths where the temperature of the ocean water is substantially lower. The land-base, atmospheric thermal process, however, is more advantageous than the ocean process, as a land-base operation requires less capital per unit of power produced, i.e. the land-base operation can be constructed in readily accessible locations using standard, well-known engineering practices and materials, and ordinary transmission lines. Ocean conversion systems, on the other hand, require off-shore installations and platforms which must withstand the massive forces encountered with wave and tidal actions. Transmission of electrical energy is by cables that are designed to be located on the ocean bottom, such cables being more costly than the conductor employed to transmit power on dry land.
In an atmospheric conversion system, the temperature differential, as indicated above, for effecting vaporization and condensation of the working medium, is related to the vertical distance between the two elevations, i.e. the height of the mountain above the floor of the valley adjacent the mountain. For example, the average difference in air temperature for a 1,000 meter change in elevation is about 10.degree. C., which is due to the cooling effect provided by the expansion of air in ascending from a lower to a higher elevation. If an atmospheric conversion system is to match the temperature differential (approximately 21.degree. C.) of a typical oceanic conversion system, a difference of 2,110 meters is required, which provides a temperature differential of about 11.degree. C. between the boiler and condenser when the two are operating to respectively evaporate and condense the working medium allowing a 5.degree. C. temperature differential in both the boiler and condenser for transfer of heat.
The weight of the material of a column of vapor (of the working medium) is supported by the pressure differential existing between the heat supply means at the lower elevation and the condenser at the upper elevation. An additional increment of vapor pressure and pressure differential is needed to overcome the friction of the vapor in the conduit connecting the evaporator to the condenser to move the vapor from the evaporator to the condenser at a rate sufficient to provide a flow of condensate for the production of useful work.
The efficiency of a conversion system of the atmospheric type is calculated as the percent of thermal (heat) input that can be recovered as work from the column of condensate (liquid) of a height corresponding to that of the vapor, this height (or distance) being fixed. Hence, for a given column height of the working medium, with its particular density and attendant pressure drop, a working medium is needed that will provide maximum efficiency in giving up its work potential to the production of useful work, such as the generation of electrical power.
However, in an atmospheric conversion system, temperature changes occur between nighttime and daytime, and with changing weather conditions. This can result in a change in the temperature differential existing between the condenser at the upper elevation and the vaporizer at the lower elevation, or a change in the temperature values at both locations with the differential staying about the same. If the temperature differential increases, vapor will be moved at a higher velocity and more energy will be lost in overcoming pipe friction, resulting in a decrease in the efficiency of the system. Similarly, the temperature differential may decrease so that vapor could not be moved through the column. The system then would not operate at all unless the composition of the working medium is adjusted to meet the new conditions.
In U.S. Pat. No. 2,499,736 to Kleen, the amount of a refrigerant (ammonia) in a cooling circuit is changed in response to ambient temperature. The purpose of such an arrangement is to control the temperature of refrigeration units on aircrafts adapted to transport food. When an aircraft is at high altitudes, the ambient temperature is low; when the aircraft is on the ground such temperature is relatively high. Obviously then, when the aircraft is flying at high altitudes, less cooling work needs to be done. There is, however, no disclosure in the Kleen patent of supporting a column of vapor extending between locations of high and low altitudes in a manner that will maintain maximum working efficiency of the column.